1. Field of the Invention
This invention relates to a new and improved control circuit for ignition systems for internal combustion engines and more particularly to transistorized ignition systems for internal combustion engines.
2. Description of Prior Art
The conventional internal combustion engine utilizes an ignition system which includes an ignition coil, or high voltage generating coil, having primary and secondary windings, the secondary winding of which is electrically coupled to spark discharge devices, such as spark plugs, or ignitors, in a predetermined sequence by a high voltage distributor which is synchronized with the crankshaft angle of the engine. The primary winding of the ignition coil is coupled to a source of voltage through a switch known as the distributor points, or more commonly referred to as points, across which is connected a capacitor. The opening and closing of the points is likewise synchronized with the engine. Ideally, the operation of this system is such that the primary winding of the ignition coil has current flow therethrough which current flow is interrupted by the points at substantially the same time that the high voltage distributor is in a position to efficiently transfer a resulting high voltage appearing in the secondary winding of the ignition coil to one of a plurality of spark plugs.
Although highly developed, the distributor points, when used directly with a high voltage generating coil, have well known disadvantages that make undesirable the use of such points in the ignition systems for internal combustion engines. For example, one disadvantage is that the distributor points are subject to continuous erosion that necessitates their frequent replacement. Also, at high engine speeds, the points tend to float or bounce due to inertia, thereby making development of the secondary winding high voltage undependable. Further, the time at which a spark takes place at the spark plug when using points in the ignition circuit may vary as a result of such factors as changes in engine speed, spring force between the points, the pitted condition of the points, friction, vibration and the like.
With the advent of reliable semiconductor components, electronic ignition control circuits have been made available to reduce deterioration of point contacts, to increase the spark plug life, to allow firing of fouled spark plugs, to eliminate high speed misses, and to provide easier starting as well as to provide other advantages.
Nevertheless, prior art ignition systems including magnetic and optical-transistor control switching circuits for triggering a charge of electricity to the spark plug have generally not worked as well as anticipated due to the difficulty of achieving a reliable switching means to trigger the high voltage ignition coil. One of the most serious problems in the prior art revolves around the circuit used to control the electronic switching in the primary of the high voltage generating coil.
It has been conventional to mount such electronic control circuits in the engine compartment wherein the circuits become vulnerable to the heat associated with the engine. Consequently, the highly temperature sensitive transistor circuits do not always insure the desired switching reliability.
Moreover, poor battery conditions or cold weather affect the amount of voltage available for starting the engine. Thus, it is desirable to provide a circuit that will be operable over a wide range of battery voltage.
Accordingly, it is an object of this invention to provide an improved control circuit for an ignition system which control circuit is least affected by variations in the voltage supplied by the vehicle electrical system.
It is another object of the invention to provide an improved ignition system which will operate over a large range of temperature extremes.
It is still another object of this invention to provide an improved ignition system which provides better noise immunity and faster overall switching characteristics than existing ignition systems.
It is a further object of this invention to provide maximum voltage across the distributor coil under varying operating conditions.
Other objects and advantages of the invention will be obvious to those skilled in the art when reference is had to the text hereof.